1. Field of the Invention
This invention relates to a device for generating an ultrasonic and high frequency sonic vibration and, more specifically, to a mechanical device capable of producing an ultrasonic and high frequency sonic vibration.
2. Background Information
Ultrasonic and high frequency sonic sound waves, or vibrations, are typically created by a transducer having a piezoelectric crystal. When an alternating current is applied to the piezoelectric crystal, the piezoelectric crystal mechanically deforms. Using this effect, a high-frequency alternating electric current can be converted to an ultrasomic wave of the same frequency, typically over 20 kHz. The piezoelectric crystal is coupled to a mechanical wave guide that transmits the ultrasonic wave into another structure. The piezoelectric crystal transducer also converts mechanical deformations into a current. That is, vibrations transmitted into the piezoelectric crystal are converted into a current. This current can be analyzed and converted into data representing the information about the structure. As such, piezoelectric crystal transducers are typically structured to provide feedback from reflected ultrasonic vibrations.
Alternatively, an electromagnetic acoustic transducer (EMAT) may be used to create an ultrasonic wave in a conductive metal. An EMAT includes a magnet and a coil disposed perpendicularly to the magnetic field of the magnet. When a current is pulsed through the coil, an eddy current is induced in the ferrous material. The Lorentz force interaction between the eddy current and the magnetic field results in a dynamic stress in a direction perpendicular to both the magnetic field and the eddy current. This stress acts as a source for an ultrasonic wave which is passed through the structure. A second EMAT, typically disposed on the opposite side of the structure from the first EMAT, is structured to receive the ultrasonic vibration and convert the vibration to an electronic signal. Variations between the vibrations produced by the first EMAT and those received by the second EMAT, which are not attributable to the structure, may indicate an internal flaw in the structure.
An ultrasonic wave in a structure may, among other uses, be used as a non-destructive means to detect flaws within the structure. As noted above, typically piezoelectric crystal transducers pick up reflections of the wave created by an internal flaw or EMAT: transducers detect variations in the sent and received ultrasonic waves. Alternatively, as shown in U.S. Pat. No. 6,236,049, an ultrasonic vibration may be used as part of a thermal flaw detection system. That is, ultrasonic waves are transmitted into an object having flaws, such as cracks. It is hypothesized that the edges of the flaws vibrate against each other and create heat due to friction. The thermal difference between the flawed and non-flawed areas may then be viewed with a thermal imaging camera. Thus, when using the thermal imaging system, the components, on the prior art ultrasonic transducers that are structured to receive data, such as the reflected wave, are not used.
Each of these means for generating an ultrasonic vibration has a disadvantage. A piezoelectric crystal has a very narrow frequency range and must have specific dimensions in order to generate a specific frequency. Additionally, the piezoelectric crystal had a limited temperature range to about 200-300xc2x0 F. The piezoelectric crystal dimensions are relatively large and, if the test object is small or has an uneven surface, the size of the piezoelectric crystal transducer may make it difficult to bring the piezoelectric crystal transducer into contact with the test object. The EMAT device, on the other hand, may only be operated with a conductive material that is capable of transmitting the eddy current and, as such, may not be used on devices such as ceramics and plastics.
There is, therefore, a need for a device capable of creating ultrasonic frequencies in a broad range.
There is a further need for a device capable of creating ultrasonic broad range frequencies that may be coupled to more than conductive materials.
There is a further need for a device capable of creating ultrasonic frequencies that is not structured to receive an ultrasonic signal so that the device may be optimized for generation of sound only manufactured at a reduced cost.
These needs, and others, are met by the present invention which provides a mechanical ultrasonic device structured to create an vibration within a range of about 5 kHz to 40 kHz. The device includes a mechanical vibration assembly and a impact member. The mechanical vibration assembly does not include a piezoelectric crystal or EMAT transducer. The mechanical vibration assembly may incorporate elements such as an AC solenoid or an electric motor coupled to a high speed eccentric cam or an eccentric shaft.
For example, in a first embodiment a solenoid having a low inertial core assembly and a coil coupled to a AC power source. Fluctuations in the magnetic field created by passing the AC current through the coil cause the core assembly to vibrate. In addition to having a low mass, the core acts as the impact member and must have a high strength in order to sustain the stress of high acceleration and impact loads. One arrangement includes a core assembly having a rigid outer jacket and a low mass ferromagnetic inner core.
A second embodiment includes a motor and an off-center disk. The motor is coupled to the off-center disk and structured to rotate the off-center disk within a range of about 5 kHz to 40 kHz. The off-center disk, which may be either a cam or a weighted flywheel, is disposed within an impact housing which acts as the impact member.
A third embodiment also includes a motor which is coupled to an eccentric shaft. That is, a cylindrical shaft having a one or more bulges extending through a discreet arc. The shaft is disposed within a hollow impact head assembly. When the motor is activated, the eccentric shaft causes the impact head assembly to vibrate.
The disclosed mechanical ultrasonic device is not structured to receive an ultrasonic signal. As such, compared to the prior art devices which are structured to receive feedback, the mechanical ultrasonic device is typically less expensive to manufacture. The mechanical ultrasonic device is intended for use with a thermal imaging system. That is, the impact member is structured to contact a test object and transmit the ultrasonic vibration through the test object.